Batteries of different chemical types, such as lithium, NiCd, and lead-acid batteries, have different voltage characteristics and different effective series resistances during the remaining time of usage. In many cases apparatus, such as radio-telephones, can use batteries of various types for their power supply. For this reason, it is useful to know various battery parameters e.g. the type, size, capacity and temperature of the battery being used, so that the proper operational parameters can be set for the apparatus, for a battery charger charging the battery, or to inform the user that the battery capacity is running out.
A battery charger may be able to charge batteries of several types, so the charger must be capable of adapting the charging rate, amongst other parameters, to the type and the capacity of the battery. Consequently, it would be useful if the battery charger could automatically recognize the type and the capacity of the battery to be charged, so that it can adapt the charging parameters accordingly.
Batteries comprise one or more electrochemical cells, supplying electrical energy by means of a chemical reaction. The type of the electrochemical cells may determine the capacity, the effective resistance, the physical set-up, or any other operational parameter. The battery may comprise several identical cells, or a combination of several different cells. The temperature of the battery could appropriately be measured in order to permit a break, for instance, during fast charging of the battery, when the temperature of the electrochemical cells exceeds a selected temperature, or to permit a break when a pre-determined voltage threshold is reached, the voltage level being temperature-compensated i.e. as a function of the temperature of the electrochemical cell.
Some battery types, e.g. those having a NiCd cell, may be damaged unless the fast charging is carefully supervised. The high temperature generated during the fast charging may cause damage to the battery, and in extreme cases, even an explosion of the battery. It is also known that charging a battery at a lower rate than its maximal rate, but at a higher rate than its minimal rate, also risks damage to the battery.
It is preferable if apparatus which can use different types of battery is able to determine the type and condition of a battery and to adapt its operating parameters accordingly. One such feature is an alarm indicating when the remaining charge of the battery is below a predetermined threshold value, the alarm being given to the user of the apparatus through the user interface connection. In this case, the battery voltage is measured in the usual way, and when the battery voltage drops below the predetermined threshold value, a light signal is switched on or the operator is given some other indication of the near-exhaustion of the useful charge. Typically, the device is allowed to operate only over a limited period of time after it has been observed that the charge state of the battery is low. A second parameter may consist of a second battery voltage threshold, which, when detected, causes the apparatus to be completely disabled and so protects those battery types, e.g. NiCd and lithium types, which cannot be discharged below a given charging level without risking permanent damage to the electrochemical cells.
Other parameters can be set according to the battery type. For instance, in cellular radio-telephones, the output of the transmitter can be set to a maximal level determined by the specific battery type used. Apart from monitoring the remaining charge, the parameter to be set according to the battery type may be a detection of the charging state, which is usually carried out in terms of the polar voltage of the battery. Batteries of different types have different characteristic curves of polar voltage-charging in relation to the remaining charge and also different charging capacity values and, thus, a predetermined and fixed voltage threshold for determining when to stop charging the battery may be optimal for one type of battery, but not for another.
In the prior art, battery temperature has been measured, for example, with a negative temperature co-efficient (NTC) resistor or individual diodes, and battery capacity has been detected either by mechanical recognition or by using separate components e.g. resistors of various sizes integrated in the battery, whereby the value of the component is measured and the battery capacity subsequently determined by comparing the value of the measured component with a stored table in a memory. Batteries of various sizes may thus have different resistors, the values of which are used to recognize the battery type. This means that separate components are needed both for battery temperature measurement and battery type identification, and this means an increased number of components and therefore an increased number of contacts between the battery and the apparatus, and, in turn a higher price for the battery and for the device to which the battery is connected.